Gold-thiol monolayers SAMs

Self-assembled monolayers (SAMs) [8] The layers are formed by heterologous interaction between reactive groups, such as thiols, and noble metals, such as gold or silver. Since the molecules are selectively adsorbed on these metals, film growth stops after the first monolayer is completed. The molecular aggregation is enthalpy driven, and the final structure is in thermodynamic equilibrium. 

M. Buck reviews in great depth the literature on self-assembled monolayers (SAMs) of thiols on gold, a classic means of surface modification. The wide variety of functional groups that is provided by synthetic chemists makes thiol-SAMs an exciting playground for applications where the gap between two worlds, the inorganic and the organic, needs to be closed. Examples are molecular electronics and biochemistry. 

While electrochemical experiments provide useful information regarding electron transport through these molecular monolayers, construction of real devices requires formation of a top contact so that solid-state transport measurements can be made. The fabrication of contacts to molecular layers has been the major obstacle to the development of molecular electronic devices, whether based on thiol-based SAMs on gold or covalently attached molecules on silicon. The most popular approach to making contacts involves evaporation of metals onto the molecular layer, which is likely to result in at least partial penetration of the monolayer, and may possibly damage the molecules in the layer. 

Self-assembled monolayers (SAMs) on gold and other metal surfaces have been extensively studied in biosensors applications.28-30 The thiol-gold chemistry is well known and is much easier controlled than organosilane chemistry (Fig. 14.4).31 34 The... 

The use of MPc complexes as electrocatalysts for the detection of analytes relies on the formation of modified electrodes. Thiol, alkylthio, or arylthio substituted MPc complexes readily form self-assembled monolayers (SAMs) on gold. Amino substituted MPc complexes can easily be electropolymerized onto electrodes. Direct adsorption of the monomer onto electrodes (especially carbon electrodes) also occurs. The modified electrodes are then employed for detection of analytes ranging from neurotransmitters, thiols, phenols, and other biologically and environmentally important molecules. 

Figure 6.5 Schematic depiction of a self-assembled monolayer (SAM) of it-hexadecane thiol (the tail group depicted in the figure is a methyl group in this case) on a single crystalline gold surface. Note the ordered nature of the SAM and the tilt of die chains, which accommodates the optimal van der Waals spacing of the hydrocarbon chains while allowing the thiol head groups to sit in regularly spaced sites on the crystalline gold surface.

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